Concept:Subsidiary Alliance was a policy used by the British to control Indian princely states through a forced treaty.
Explanation:This system was devised by Lord Wellesley, the Governor-General of India from 1798 to 1805. So option A is correct.
Under this alliance, an Indian ruler had to disband his own army and accept British troops in his territory.
The ruler also had to pay for the maintenance of the British army. If payment was not made, a part of his territory was taken away.
In return, the British promised to protect the state from foreign attacks and internal revolts.
Thus, the Indian ruler lost control over foreign affairs and military, becoming a British protectorate.
The Nawab of Awadh was the first ruler to enter into this alliance after the Battle of Buxar.
The Nizam of Hyderabad was the first to accept a well‑framed subsidiary alliance.
Note that the French Governor‑General Marquis Dupleix actually used this concept first.
Answer:Lord Wellesley.